1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a multi-domain vertical alignment (MVA) liquid crystal display device.
2. Description of the Prior Art
Because the liquid crystal display (LCD) device has advantages of thin appearance, low power consumption, and low radiation, the LCD device has been widely applied in various electronic products such as computer monitors, mobile phones, personal digital assistants (PDAs), and flat panel televisions, etc. In general, the LCD device comprises a liquid crystal layer encapsulated by two substrates. The operation of an LCD device is featured by varying voltage drops between opposite sides of the liquid crystal layer for twisting the angles of the liquid crystal molecules in the liquid crystal layer so that the transmittance of the liquid crystal layer can be controlled for illustrating images with the aid of the light source provided by a backlight module.
However, the viewing angle of a conventional LCD device is not sufficiently wide to ensure high display quality, therefore limiting the development of LCDs. For that reason, a multi-domain vertical alignment (MVA) LCD device is made to increase the viewing angle. A 4-domain vertical alignment LCD device was initially developed for achieving a wide viewing angle image display. In the structure of the 4-domain vertical alignment LCD device, each pixel unit has only one sub-pixel unit, which results in a color washout phenomenon occurring to an oblique viewing angle of the 4-domain vertical alignment LCD device. For that reason, an 8-domain vertical alignment LCD device is developed for solving the color washout problem. In the structure of the 8-domain vertical alignment LCD device, each pixel unit includes two sub-pixel units for achieving a feature of wide viewing angle without an occurrence of the color washout phenomenon. That is, based on gray level averaging effect of two gamma curves corresponding to the two sub-pixel units, optimal visual experience can be realized in different viewing angles, for achieving a high-quality wide viewing angle image display.
FIG. 1 is a circuit diagram schematically showing a prior MVA liquid crystal display device. As shown in FIG. 1, the liquid crystal display device 100 comprises a pixel unit 180, a data line Dn, a data line Dn+1, a gate line Gma, a gate line Gmb, and a storage capacitor line (also termed as a common line) 190. The pixel unit 180 comprises a first sub-pixel unit 110 and a second sub-pixel unit 120. The first sub-pixel unit 110 includes a thin film transistor (TFT) 115, a liquid crystal capacitor Clca, and a storage capacitor Csta. The second sub-pixel unit 120 includes a thin film transistor 125, a liquid crystal capacitor Clcb, and a storage capacitor Cstb. The thin film transistor 115 is electrically connected to the data line Dn and the gate line Gma. The thin film transistor 125 is electrically connected to the data line Dn and the gate line Gmb. Although the LCD device 100 is able to achieve an MVA wide viewing angle image display by controlling the transmittances of the first sub-pixel unit 110 and the second sub-pixel unit 120 through making use of the date signals delivered by the data line Dn, the pixel unit 180 requires two gate lines Gma and Gmb for providing two gate signals so as to control two thin film transistor 115 and 125. That is, the number of gate lines required by the LCD device 100 is twice the number of gate lines required by a conventional LCD device, and therefore the aperture ratio of each pixel unit in the LCD device 100 is significantly reduced. Furthermore, the frequency of driving clock used in the LCD device 100 is also twice the frequency of driving clock used in a conventional LCD device. For that reason, compared with a conventional LCD device, the LCD device 100 is rather costly, and the operation power consumption is increased significantly.
There is another prior-art MVA liquid crystal display device having each pixel unit electrically connected to just one gate line. However, regarding this prior-art MVA liquid crystal display device, one of two sub-pixel units in each pixel unit has a floating electrode, and therefore a phenomenon of static charge accumulation is likely to occur during a long-term operation, which in turn causes an occurrence of permanent image sticking effect and the image display quality is then degraded significantly.